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A295393 Numbers k such that 5*10^k + 23 is prime. 0
1, 2, 3, 4, 10, 11, 15, 43, 51, 110, 164, 303, 824, 3160, 4994, 8596, 11717, 22370, 22600, 65509 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 23 is prime (see Example section).

a(21) > 10^5.

LINKS

Table of n, a(n) for n=1..20.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 50w23

EXAMPLE

2 is in this sequence because 5*10^2 + 23 = 523 is prime.

Initial terms and primes associated:

a(1) = 1, 73;

a(2) = 2, 523;

a(3) = 3, 5023;

a(4) = 4, 50023;

a(5) = 10, 50000000023; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[5*10^# + 23] &]

PROG

(PARI) isok(k) = isprime(5*10^k + 23); \\ Michel Marcus, Nov 22 2017

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A047455 A202426 A039002 * A120023 A115897 A116019

Adjacent sequences:  A295390 A295391 A295392 * A295394 A295395 A295396

KEYWORD

nonn,more,hard,changed

AUTHOR

Robert Price, Nov 21 2017

STATUS

approved

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Last modified January 21 20:08 EST 2019. Contains 319350 sequences. (Running on oeis4.)